My application displays a column which shows if tasks are delayed or not and how big the delay is. The delay may be positive (if a task is delayed) or negative (if it's on time). The time difference between now and the scheduled date is shown.

I'd like to describe this column in a short way. How to call something opposite to delay in this case? Ahead? Advance?

What's wrong with 'delay'? If the delay is negative, which os probably rare, then you're ahead in the schedule; 'delay' is good for positive and negative.
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MitchMay 14 '12 at 11:53

It was unclear for some users that this column may show negative and positive delay as well.
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alekwisniaMay 14 '12 at 13:00

You will have to look for a new set of complementary terms for +ve and -ve values -- not a pairing word for 'delay'.
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KrisMay 14 '12 at 13:07

1

More clarification is needed. Is this like 'hot', 'cold', 'temperature', and instead of an analogy for 'hot', you want the anlog of 'temperature' for time? Or maybe 'right', 'left' 'position'?
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MitchMay 14 '12 at 14:11

Mitch: good example. Temperature could be below and above zero. The thing I need is before or over some point in time.
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alekwisniaMay 18 '12 at 9:31

What you are measuring is timeliness. If something is on time it's being delivered in a timely fashion; if it's delayed it's not timely.

As well as being on time, a task can be ahead of schedule, which indicates that it will be finished before its due-date. If it's on time, with (say) two days' work to do in the next two days, then it's not ahead — even though your application will show −2.

However while the concepts of "days to go till the deadline" and "days overdue" can be expressed by positive and negative numbers (either way round), if what you're after is a heading for the column then I'd suggest just T. This means that you could read it is "Task X is at T − 5" or five days till its due date, or "Task Y is at T + 2" meaning it's two days overdue. "T" used in this way means "the due date" or "the due time" and it's caricatured in rocket launch countdowns, "T minus 10, 9, 8..."

What I actually mean is how to call the column, so that it clearly describes content. I thought about "Delay/ahead" or "Delay/advance", but I'm not sure about this second word. Or maybe there's one short phrase that describes both.
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alekwisniaMay 14 '12 at 10:51

However, what you've said in your last paragraph is interesting - is this some kind of standarized notation?
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alekwisniaMay 14 '12 at 10:54

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The use of T in connection with rocket launching and with negative and positive numbers is described in Wikipedia with credible attributions, so I guess it is.
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Andrew Leach♦May 14 '12 at 11:18

I can't cite a source on this, but I believe "T" is normally used for time, i.e. a span of hours or minutes, while "D" is used for days, as in "D-3" meaning 3 days until the event. But that said, I've seen this notation used to refer to time until an even is scheduled to occur, but not for deviation. i.e. in a rocket countdown, "T-10" means 10 seconds to lift off, not that the liftoff is 10 seconds behind schedule.
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JayMay 14 '12 at 15:31

No, but T+10 is 10 seconds after liftoff is supposed to have happened, whether it was slightly off or not. It's true D is generally used for days ("D-Day" was thus named), but using T in the manner described is probably understandable by analogy -- especially since the OP is using minus until the due day and plus after it.
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Andrew Leach♦May 14 '12 at 15:38

I can't think of a single word that expresses this idea and where the meaning of the sign would be clear.

I think the best you're going to do is something like Charles W's suggestion: a two-word title like "Ahead/Behind" or "Early/Late". I'd add that you should probably give some notation to indicate which is a plus and which is a minus. Like, I'd probably make the heading "Ahead(+)/Behind(-)" (or the other way around, whichever way you want to express it).

If it's for technical people, it's common to refer to deviations as a "delta", so you could call it "Schedule Delta". But you'd still have the issue of clarifying whether a positive number means you're ahead or behind.

Unless you have an established convention, I'd make positive mean ahead of schedule, just because we normally think of positive numbers as being good and negative numbers as being bad. Not always, but usually.

I've had this problem a few times - trying to present a field that we think of in code as being one thing whereas non-programmers would find the concept we're trying to express as being at best misleading, confusing or simply wrong

I think the concept you're describing is more akin to "OnTarget", "Expected" or "ETA".